Effects Of Interaction Between Nitrogen Forms And UV-A On Physiological Characteristics Of Purple Lettuce(Lactuca Sativa L.)

In order to improve the yield and quality of purple lettuce,and reduce the nitrate content,we used purple lettuce?Lactuca sativa L.cv‘Zhongshu Purple Lettuce'?as material,adopts the hydroponic nutrient solution method,and LED intelligent light control console as light source,by adding different ratios of NO₃^--N and NH₄⁺-N to the nutrient solution,and adding20?mol·m^-2·s^-1 UV-A based on white:red:blue light(130:120:30?mol·m^-2·s^-1),the effects of different NO₃^--N/NH₄⁺-N ratio?NO₃^--N,NO₃^--N/NH₄⁺-N=3:1,NH₄⁺-N?and UV-A interaction on yield,quality,photosynthetic characteristics,anthocyanins and nitrogen assimilation of purple lettuce were studied.The appropriate NO₃^--N/NH₄⁺-N ratio and UV-A dose were determined to provide a theoretical basis and technical parameters to produce hydroponic purple lettuce under controlled environmental conditions.The main findings are as follows:1.After adding 20?mol·m^-2·s^-1 UV-A,the treatment of NO₃^--N/NH₄⁺-N?3:1?increased the growth,photosynthetic rate,chlorophyll content of purple lettuce,while treatment with NH₄⁺-N the net photosynthetic rate and chlorophyll fluorescence parameters were significantly reduced,which caused damage to the PSII response center,produced photoinhibition,and was not good for the growth of purple lettuce.2.After adding 20?mol·m^-2·s^-1 UV-A,the content of soluble sugar,soluble protein,free amino acids,total phenols and flavonoids were highest under the treatment of NH₄⁺-N,the treatment of NO₃^--N/NH₄⁺-N?3:1?helped reduce the nitrate content in purple lettuce,and under the treatment of NO₃^--N,the nitrate content increased significantly.3.20?mol·m^-2·s^-1 UV-A significantly promoted the activity of key enzymes related to anthocyanin synthesis and increased the content of anthocyanins in purple lettuce.Under the treatment of NO₃^--N/NH₄⁺-N?3:1?,the anthocyanin content of purple lettuce increased significantly,while the treatment with NO₃^--N was the lowest.4.At different NO₃^--N/NH₄⁺-N ratios,ammonium nitrogen increased the accumulation of reactive oxygen species and malondialdehyde?MDA?content,but also increased proline?Pro?,superoxide dismutase?SOD?activity,peroxidase?POD?activity,and catalase?CAT?activity.The addition of 20?mol·m^-2·s^-1 UV-A significantly reduced the content of active oxygen and CAT under different nitrogen forms,the MDA content was significantly reduced under the treatment of NO₃^--N/NH₄⁺-N?3:1?.At the same time,it increased the activity of antioxidant enzymes and non-enzymes to prevent membrane lipid peroxidation.5.Adding 20?mol·m^-2·s^-1 UV-A and NO₃^--N/NH₄⁺-N?3:1?treatment significantly increased the nitrogen assimilation ability of purple lettuce leaves and accelerated the function of nitrogen metabolism in plants.Further increase the content of soluble protein and free amino acids in the plant,and promote the accumulation of biomass.